Lead and zinc are often found as a mixed sulphidic ore. Sulphidic ore bodies containing lead and zinc may also contain sulphides of copper and iron, as well as gold and silver. Recovery of lead and zinc from such mixed sulphide ores has been achieved by a number of different processes. For example, the ore may be treated to form a concentrate of enhanced lead and zinc content and concentrate may be subjected to other metallurgical processes, such as smelting, to recover lead and zinc metal.
Alternatively, treatment of such ores typically involves a number of flotation steps to recover a high-grade lead concentrate and high-grade zinc concentrate. The high-grade lead concentrate is then treated to recover lead and the high-grade zinc concentrate is then treated to recover zinc.
Hydrometallurgical processes have also been used in which the ore or concentrate is leached with sulphuric acid whereby the zinc sulphide is dissolved (in the form of zinc sulphate) in a leaching solution, with zinc being recovered using an electrowinning process.
Several processes for treating mixed sulphidic materials are set out below:
U.S. Pat. No. 3,954,450 discloses contacting lead sulphide material with an aqueous medium containing aqueous sulphate and free ammonia. The slurry is introduced into a reaction vessel and oxygen is introduced to the vessel. The sulphide is converted into substantially water insoluble oxidic lead compounds whilst any zinc present is dissolved. The zinc-containing solution is separated from the solids residue and the solution is treated to recover zinc metal. The residue is subject to froth flotation and lead reports to the tailings. The lead-containing tailings are treated to recover lead metal. The concentrate from the froth flotation step contains iron sulphide and may be discarded or sent to treatment to recover iron.
U.S. Pat. No. 4,063,933 describes a process for treating a sulphide concentrate containing lead, copper, zinc and silver to selectively recover these metals. The process comprises contacting the concentrate with sulphuric acid in the presence of oxygen at elevated pressure and temperature to extract copper and zinc from the concentrate (by dissolution as soluble sulphates), followed by recovery of copper and zinc from the solution. The leach residue (which contains lead) is contacted with lime to remove sulphur. Subsequently, the leach residue is contacted with a mixture of calcium chloride and ferric chloride to extract lead and silver.
U.S. Pat. No. 4,545,963 describes the separate recovery of zinc and lead values from zinc and lead containing sulphide ores that also contain iron. The process comprises grinding the ore, subjecting the ground ore to a first flotation step to float an initial lead concentrate containing zinc and to produce a zinc and iron containing tailings. The zinc and iron containing tailings is subjected to a second flotation step to float an initial zinc concentrate and produce a tailings. The initial zinc concentrate is then subjected to a third flotation step to float a further zinc concentrate containing iron and also produce a zinc and iron containing tailings. The tailings from the third flotation step and at least the lead and zinc containing portion of the initial lead concentrate is leached under oxidising conditions at a temperature of from 130 to 170° C. in aqueous sulphuric acid to produce a lead containing residue and a first leach solution containing zinc and iron. The acid leaching step results in the dissolution of zinc, which can be subsequently recovered using electrowinning.
U.S. Pat. No. 4,568,525 describes a method of producing a zinc sulphide containing concentrate from a mixed lead-zinc concentrate. This process involves selective leaching of lead using a ferrous chloride solution with an oxygen containing gas being bubbled through the leaching solution. The lead sulphide is converted to lead chloride, which either dissolves into solution or forms lead chloride precipitate, which can then be separated from the zinc sulphide by any physical technique such as flotation. The selectivity of conversion of lead sulphide to lead chloride is enhanced by conducting the leaching step using a relatively coarse granulometry of the feed material, with a particle size distribution of the feed material having a d80 of greater than about 200 μm being preferred.
International patent publication number WO 96/07762 describes leaching of mixed concentrates in an autoclave by oxidising sulphur components in the feed to produce sulphuric acid in-situ. The slurry resulting from the leach is neutralised and metals are removed by known processes after the slurry has been subjected to a solid/liquid separation step. The conditions used in the autoclave include temperatures of at least 180° C. and pressures in the range of 2 to 8 atm.
International patent publication number WO 96/15279 describes the mechanical activation of sulphide minerals to induce chemical reactions between sulphide minerals and certain reactants at low temperatures which cause the chemical breakdown of sulphide grains. The main focus of the specific embodiments of this patent relate to the treatment of ZnS containing powders. Copper oxide is mixed with the ZnS to form zinc sulphate according to the following reaction:ZnS+8CuO→ZnSO4+4Cu2O
The soluble zinc sulphate is separated from the insoluble copper oxide by leaching with water.
Mixed sulphide ores are also treated by the “Albion Process”. The Albion process was developed by MIM Holdings (now Xstrata Plc) and is being commercialised by Xstrata Technology. The process involves an ultrafine grinding of a mineral or concentrate, followed by oxidative leaching at atmospheric pressure in conventional agitated tanks.
Zinc concentrates may be treated in the Albion process to produce a leach solution containing dissolved zinc and a leach residue solids containing other oxidised material. Zinc can be recovered from the leaching solution using electrowinning.
The Albion process has also been used to recover gold, copper and silver.
Throughout this specification, the term “comprising” and its grammatical equivalents shall be taken to have an inclusive meaning unless the context of use indicates otherwise.
The present applicant does not concede that the prior discussed in this specification forms part of the comment of knowledge in Australia or elsewhere.